Dranesville, under Major Taggart, I ordered to move on Fairfax Court-House. It came in contact with the enemy at Frying Pan, and drove in their advance, but could make no impression on their main body. Colonel Wyndham also fell on their rear near Chantilly, but for the same reason could not do them much injury. He overtook them this side of Chantilly, and, although having only 500 men, made them deploy their force, and found them to number over 3,000 men. His advance followed them as far as Pleasant Valley. When I ordered the infantry to Annandale, I had but little hope of their getting there in time to intercept the enemy, but thought the chance worth trying. The rebels entered our lines by an attack on Dumfries, where they were repulsed; then passed on toward the Occoquan, and were most gallantly met by our cavalry, but their force was overwhelming. It was not possible to hold the river-fordable at a number of places. After crossing the Occoquan, they found every point so well guarded and all our troops on the alert that they could only seek for an outlet for escape. This their heavy force and knowledge of the country enabled them to accomplish. Their escape was not owing to any negligence on the part of our pickets or outposts, as every one was on the alert and vigilant.

Respectfully submitted.

S. P. HEINTZELMAN,

Major-General, Commanding.

General G. W. CULLUM,

Chief of Staff, U. S. Army.

P. S.-Lieutenant David H. Leche, of the Second Pennsylvania Cavalry, on the other side of the Occoquan, made a gallant and determined charge with but 25 men upon a rebel regiment, and behaved so well as to elicit the praise of the rebel general. He was, unfortunately, killed, as was also Lieutenant T. G. Snyder, of the same regiment. I have no information as to the disposition of our troops beyond the Occoquan. When General Slocum withdrew his troops from Wolf Run Shoals I sent some to occupy it.

[Inclosure.]

HEADQUARTERS DEFENSES OF WASHINGTON,
December 28, 1862.

Brigadier-General ABERCROMBIE:

GENERAL: The major-general commanding directs that you send three regiments and one battery from Upton's Hill to occupy Annandale, and three regiments and one battery from Minor's Hill to take post about half way between Falls Church and Fairfax Court-House, in such position that they can readily support the troops at Annandale. This movement is to endeavor to intercept a rebel force reported to have crossed the Occoquan, between 4,000 and 8,000 strong (infantry, artillery, and cavalry), and which, it is believed, will attempt to retreat between Alexandria and Fairfax Court-House. Colonel Swain has been directed to report to you, with all his disposable cavalry, at Arlington. Major Taggart has been ordered to move with his cavalry force from Dranesville toward Fairfax Court-House. The line from Fairfax Court-House south to the Potomac is held by General Stoughton, Colonel D'Utassy, and General Slocum. General Abercrombie will take command of this movement in person, and will establish his headquarters at Annandale, where the different commanders will report to or communicate with him. The troops will move at once, and should be in posi-